Question

Suppose a laboratory has a 31 g sample of polonium-210. The half-life of polonium-210 is about 138 days. How many half-lives of polonium-210 occur in 966 days? How much polonium is in the sample 966 days later?

Answer 1

Number of half-lives = how many times 138 days 'goes into' 966 days.
`(966)/(138) = 7` so 7 half-lives occur in 966 days.

Every half-life, the substance decays by exactly half of its original mass so we need to halve 31 seven times.
`(31)/(2 * 2 * 2 * 2 * 2 * 2 * 2) = (31)/(2^7) = 0.242g`